NAPLES — Midway through what's normally peak season for West Nile encephalitis, Southwest Florida is dormant.
The Collier County Mosquito Control district hasn't had a single positive test among surveillance mosquitoes to monitor for the disease, which can cause brain swelling and potentially serious neurological symptoms in humans.
Lee County mosquito control officials have had a few positive tests among surveillance chickens used to monitor for diseases.
The test results of both mosquito control districts are provided to health officials in the two communities so they can alert the public, when deemed necessary, to take measures to avoid exposure to potentially infected mosquitoes.
So far this year in Lee, three surveillance chickens have tested positive for West Nile and five chickens have tested positive for St. Louis encephalitis, which also is transmitted to humans by mosquito bites from infected mosquitoes, said Jim Burgess, manager of mosquito and disease surveillance with the Lee mosquito control district.
"It's all up in the Panhandle," Burgess said of Florida's West Nile. "It's just slowly taking its time to come down (the state)."
What's more typical is 20 or more monitoring chickens testing positive for West Nile in a given week during peak season, he said, and that's way down from the norm of 50 to 60 positive test results in the 1970s and 1980s, Burgess said.
He also points out that by the time blood test results are back from chickens and there's a confirmation from the state laboratory, the mosquito control district has done aerial insecticides to combat mosquitoes.
The primary carrier for West Nile and St. Loius encephalitis in Southwest Florida is the freshwater Culex nigripalpus mosquito. So far, monitoring in Collier has turned up a high concentration of that breed of mosquito in eastern parts of the county but none have been positive for the disease, said Adrian Salinas, spokesman for Collier mosquito control.
"I wouldn't say it is unusual," Salinas said. "There isn't any science to it but we are experiencing a high number of Culex, especially in Golden Gate Estates."
The last human case of West Nile in Collier was in 2010 when two older men contracted the disease and one of them died, said Deb Millsap, spokeswoman for the Collier County Health Department.
Southwest Florida's nonexistent encephalitis season this year is in stark contrast to the West Nile epidemic in the U.S., with 3,545 human cases and 147 deaths so far through Sept. 25, according to the U.S. Centers for Disease Control and Prevention in Atlanta.
It is the highest level reported to the CDC since 2003. More than 70 percent of cases are concentrated in eight states, with Texas at the top with 1,355 human cases and 52 deaths, according to the CDC. Other states with numbers are California, Illinois, Michigan, Mississippi, Oklahoma, South Dakota and Louisiana.
Florida's 44 human cases of West Nile, with two deaths, have been concentrated in the Panhandle but it is starting to head to Tampa and the Indian River area, Burgess said.
Dr. Larry Murphy, an incumbent Lee County mosquito district commissioner who is seeking re-election, wants to make sure the public is informed of monitoring and positive test results in chickens. So he's asking officials with the Lee health department to explain at the district's meeting Thursday how they decide when to issue press releases about positive results.
"I want to find out from the health department what their protocol is," he said.
County health departments have protocols for when they issue press releases about the presence of West Nile in sentinel chickens or mosquitoes. Factors include when the infection rate is higher when compared with historical levels, or two or more confirmed cases in horses for equine encephalitis, or a human case that was locally acquired.